Fixed nav on scroll

script.js

	var nav_offset = $('nav').offset().top,
		nav_height = $('nav').outerHeight(true);
	$('nav').after($('<div>').addClass('padding').css('height', nav_height));
	$(window).scroll(function(){
		if ($(this).scrollTop() > nav_offset){
			$('nav').addClass('fixed')
		} else {
			$('nav').removeClass('fixed')
		}
	});

style.css

nav.fixed {position: fixed;top: 0;width: 100%;z-index: 1000;}
nav+.padding {display: none;}
nav.fixed+.padding {display: block;}